Enhanced Emission in Core@Shell Heterostructure of 3D Halide Double Perovskites

Inorganic metal halide double perovskites (HDPs) have successfully addressed the toxicity and instability concerns of lead-based perovskites. However, they still have to bridge a significant gap to obtain the desired optical properties. The fabrication of core@shell heterostructures is a well-known method for tuning the optical properties of materials; a technique yet to be explored for metal HDP nanocrystals (NCs). Nevertheless, the growth of core@shell perovskite nanocrystals is difficult because of the softness and ionic nature of the perovskite lattice. Here, we present a facile colloidal technique for the growth of a lead-free Cs₂NaInCl₆ shell on the surface of Cs₂AgBiCl₆ cubic NCs. This process leads to ten-fold enhancement in photoluminescence quantum yield (PLQY) immediately and the PLQY keeps increasing with time. Optical measurements reveal the formation of new emissive states attributed to alloy formed at interface and carrier dynamics are investigated using time resolved PL and transient absorption data. This method of heterostructure formation is a remarkable approach to tune the optical characteristics of lead-free halide double perovskites.